The statistics of earthquakes in Southern California

abstract A statistically significant series of earthquakes in Southern California, 1934-1957, variously filtered to avoid aftershocks and events outside a localized area, has been tested for a Poisson distribution. It has been found that, for any of several methods of filtering, the data do not fit a Poisson distribution and hence a causal connection between weak earthquake events is inferred. The conclusion is in accord with that of Aki for large events.